It’s funny. I somehow read what you wrote as “I have no argument to the contrary”

• two party system is kind of a misnomer, there’s plenty of other parties and potential parties in the US, a lot of which would theoretically correspond to larger parties in more healthy democratic states. The difference is that since the US operates on plurality voting, only two parties are ever going to have major influence in any electoral area, some countries like Canada and the UK have more diverse political ecosystems, but that’s born more out of the ability of parties in both to form voting coalitions. In the US the Democrats and Republicans each encompass big tents that hold several groups that would otherwise be their own political parties.

• It’s less that they’re both popular and more that nobody is capable of organizing a meaningful alternative unless it happens to be during the one time of the political season when you really should have the alternative well established already. Both parties have been around for over a century now and have proven ideologically flexible enough to avoid the doom of prior parties like the Federalists, Democratic-Republicans, and Whigs that had previously held one of the two top spots.

I see a likely future where some great mechanism of upheaval will bring about a nation spanning voting reform in the US, and when that happens the Dems and the Republicans will likely remain as the two top players but now amidst a large field of options that are able to compete with one another without spoiling elections for the overall wing of the political spectrum they lay within, longer term would be harder to predict as those kinds of democracies haven’t existed for long enough to observe how parties shift change and move forward and backward relative to one another over a more extended period than a few decades.